Concrete screeding devices are used to finish freshly poured concrete pavements. Freshly poured concrete contains aggregate, cement, and entrained air, and requires smoothing. The concrete is commonly poured between forms at either side of the roadbed. Finishing is accomplished by use of a vibrating screed. The screed is typically formed of a beam or truss structure which spans and sits atop the concrete forms on either side. Long span screed structures are formed of abutting shorter sections attached together longitudinally. The bottom of the structure includes a bottom plate having a smooth screeding surface which smooths the concrete.
A motor is commonly mounted on the screed to provide a source of vibration. Vibrations are transmitted to the screed structure which transmits the vibrations to the concrete below via the screeding surface. The device is pulled laterally over the concrete, either automatically or by an operator on either side. As the screed is moved over the concrete, the concrete liquifies and slumps in response to the vibrations and smoothing actions of the screed. The vibration may be transmitted from the motor directly to the screed frame, which results in poor vibration and poor concrete finish in areas remote to the vibratory motor. The vibration may be distributed over the screen length by a drive shaft with eccentric weights. Such a shaft and any associated bearings and pulleys can become fouled with wet then dry concrete.
The finished concrete should be both substantially level relative to the earth and have the desired surface contours. Desire contours include having the center higher than the shoulders, "a crown", and having the center lower, "an invert." Screeds must therefore be adjustable such that the bottom screeding surface assumes an upward and downward camber, respectively. Screeds require time to align and interconnect for the desired surface, and can come out of alignment during use, due in part to the vibrations and poor connection between sections. A system for monitoring alignment in use would be desirable.
Screeds are formed of short sections to allow transportation to work sites. The sections must be attached together so as to provide a rigid structure capable of delivering the desired surface contour. In particular, the sections must be attachable to create smooth crowns and inverts, as well as flat surfaces. Loss of rigidity can cause a vertical bowing of the structure, resulting in the center portion drooping. Loss of rigidity can also cause a lateral bowing of the screed structure, with the center portion lagging laterally behind the end portions. Lateral bowing can cause the center portion bottom plate to angle into, or "toe into" the concrete, causing the leading edge to dig into the concrete to be smoothed. This is less than desirable behavior, defeating the smoothing function of the screed.
Sections must be attachable in such a way to allow sufficient freedom to achieve the desired surface contour, while providing needed rigidity. Currently available methods for attaching sections together utilize short, vertically oriented connecting plates having holes, for bolt attachment to vertical angle iron sections on adjacent screed sections being abutted. The attachment plates provided are not attached to the horizontal, screed bottom plate as any bolts through the bottom plate would mar the concrete finish. The reliance on attachment to vertical surfaces only is inherently rigid in one dimension but weak in others.
The use of bolts for attachment close to wet concrete on a vibrating device results in bolts being covered with wet, then dried, and therefore extremely abrasive concrete. When the concrete dries it becomes difficult to remove the dried material, and, consequently, it becomes extremely difficult to remove assembly bolts and nuts which become encrusted. It will be seen then that one significant problem is that disassembly can become virtually impossible.
The constant vibration of the vibratory motor can also cause fatigue and eventual failure at the point of attachment between bolt, connecting plate, and screed section. Concrete dust between bolt and the surrounding holes in plate and screed sections acts as a grinding agent, wearing the holes larger, increasing play between bolt and hole, causing more fatigue. Increased play between screed sections causes the screed bottom plate camber to come out of adjustment. This in turn makes continual alignment checks desirable.
What remains to be provided is an improved means for attaching two screed sections together which is rigid, allows for a smooth bottom plate, and which is not easily fouled by wet cement. What has not been provided is a system that distributes vibrations over a screed that is not easily fouled. What would also be desirable is an easy to use system for monitoring screed section alignment during use.